text:
Is there a symbols chart or legend for common aerospace equations?
I've read a lot of answers on this site that make references to various aerospace equations.
So many of these are awesome responses, but I have trouble understanding the math because I don't know what all the symbols in the equation mean, or what units they are referring to.
For example, this question uses the equation below and even has a really cool picture to go along with it:

However when trying to understand the "mass flow" function I didn't see any explanation of what the lowercase "t" variable was.
I am sure this is common knowledge for many people, but are there are any charts out there for amateurs like myself to understand the different symbols commonly used in fluid functions and their implied units?
Or is this really a matter of needing to learn aerospace in general as the equations are too diverse to understand by a symbols cheat sheet?

I don't really understand what you are trying to ask: Symbols chart for common aerospace equations is not a question

Sorry, I edited the question to reflect more what I meant.

I would consider you adding a source link for the picture above

@FallenUser I did, I added a hyperlink to the "for example this question" that leads you back to the question. I'll edit it to make it more obvious

Even if they do make it to the question, you should add where it came from as the question with the picture does not

dm/dt is a derivative function which in this case means the derivative of mass with respect to time. This is basic calculus, not really related to aviation.

Learn physics. Even if we tell you the names, you will not understand it without the underlying concept.

Unfortunately, the nomenclature used can vary from source to source, and the same variables can even be used for completely different things depending on the context. It is generally good practice for the author to describe the variables they use, but we've all been guilty of skipping that step.
In any case, there are many helpful sites such as See How It Flies or the Aerodynamics Index from NASA that tend to use pretty 'standard' notation. BUT, there is no single cheat sheet that has every variable for every analysis and one should always be careful to double check.


text:
Is there less vertical space for an engine under the wing of a 737 Max than for an A320neo?
The source of this question is the understanding that the LEAP-1B couldn't fit under the wing of a 737 without changing its longitudinal position. But this wasn't the case with the design of the LEAP-1A/A320neo. For lack of ground clearance?
What is the height under the wing of a B737 Max at the point where the engine is attached? Under the wing of an A320neo?
Regarding question duplicity: This is about wing ground clearance, not engine ground clearance.

welcome to aviation.SE. I'm sorry, but I think that the "this matter" part only distracts from the question. I've edited it out so that the answers can concentrate on the important fact without needing to cater to any speculation.

Possible duplicate of Why are the Boeing 737 nacelles odd shaped?

@fooot I disagree, this is a totally different question. plus, the 737 Max does not have a such odd shape: https://www.airliners.net/photo/Boeing/Boeing-737-8-MAX/2745186/L

@Federico It's just the angle of your picture. The LEAP on the MAX has the same offset gearbox to flatten the nacelle the CFM56 does.

It is well established that there is less clearance under a 737 versus the A32x series.

Possible duplicate of Is the ground clearance of the B737 engine low compared to similar aircraft?

The question is about the ground clearance of the wing, not of the engine. I'd like to understand why during the design of the 737 Max they had to offset the engine. The result of offsetting the engine would be to get the engine clearance back to "normal", because of a low wing clearance.

The short answer is:
Yes, there is less vertical space under the wing of a 737 Max compared to an A320neo.
In the image below I have put the two airplanes side to side and the height difference is very apparent. Please note that the images are from the respective predecessors of the aircraft. The only thing that has changed regarding the height is that the 737 MAX has slightly larger tires than the 737 Classics, which should raise the MAX by 2 inches.
The reason for the lower height of the 737 is that it was developed a lot earlier when engines were a lot smaller in diameter. Therefore, they designed shorter landing gear. Choosing longer landing gear would have seemed unreasonable because this comes with a significant weight penalty. Redesigning the landing gear now would basically mean designing a completely new aircraft, because it would interfere with so many other systems.

Image Source A320, Image Source 737
It is difficult to accurately compare distances in photographs, because they come with all kinds of distortions. I have resized the images so that the main gear track is according to scale. Therefore the height comparison of the wings is fairly accurate.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
What are the "certain" flying scenarios in which the Boeing MCAS is supposed to assist pilots?
Boeing bulletin issued last November said

"MCAS provides automatic nose-down inputs to assist pilots in certain
  manual, flaps-up flying scenarios, especially at slow airspeeds and
  high AOA."

John K provided a complete and detailed answer.  Thank you.  Since altitude is not significant, I have amended the question to be more appropriate for this site.

what research have you done before asking this question?  There's been a lot of information put out regarding that system since the Lion Air accident in October of 2018. It took me a while to realize where your quote stopped, so I tossed in a quote block.  If you have a link for that source, it would be  great.

Oh, where are my manners?  Welcome to Aviation.SE. Please take the [tour] to see how an SE site is different from a forum.  Also take a look at how to ask questions and how to write answers.

How do you interpret the quoted text to mean high altitude?  Slow airspeeds and high AOA sounds like an initial climb-out to me, not a high altitude cruise.

Shoudn't that be 'high attitude'? As in high AOA?

Edited the question to be more appropriate for this site.

MCAS is basically an artificial stability system for the flaps-up low-speed regime, autopilot off, that is what I would call clever a band-aid solution to a pitch instability problem that showed up in development.
If you are hand flying at low speed and are trimmed at, say, 190 kt flaps up, and the airplane is on trim speed, the nose should be rock solid and not wander up or down on its own unless speed (or thrust) changes occur.  If you are going 190kt and decelerate to 180, the nose should pitch down and vice versa if you accelerate (thrust being constant - thrust changes also change trim speed because it applies leverage to pitch the nose up, but let's not complicate things).
With the Max in that sort of configuration, hand flying, slow, flaps up, the pitch behavior didn't meet cert requirements and the nose would typically drift up on its own, which, if thrust is the same, raises AOA and makes the airplane slow down when it should be holding a constant pitch attitude and speed.  This makes the airplane a handful to hand fly at low speed because the pilot has to actively make inputs to stop the drift in pitch, which really raises the workload (fly any other airplane with the C of G too far aft and you get something similar).
Soooo, they decided to use computers to run the horizontal stab in the background, transparent to the crew, to do the job of stopping the drift in pitch attitude and make the airplane behave the way it naturally should - an artificial stability system, but whose role was limited to fixing this particular characteristic in this particular configuration.
The alternative would probably have involved making the horizontal tail larger, which would have resulted in the usual cascade of side effects and really upset the apple cart of the development business case for the Max.  A classic case of a software based fix for a thorny aerodynamic problem that avoids dealing with the actual aerodynamic problem because dealing with the actual problem might have blown up the program during development.
From what I understand it's related to the new engines, which have more power and hang lower and whose thrust line has more pitch up leverage as a result, and which reduces the down force required of the horizontal tail, similar to moving the CofG aft, among other factors (it's the tail's downforce balancing the center of gravity forward of the center of lift, an aerial see-saw you might say, that is where pitch stability comes from).

Thanks for the last paragraph. That answered the question that was developing in my head as I read the rest of the answer.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is prop RPM control logic on PC-12?
Pilatus PC-12 has a constant speed propeller, but it does not have a prop control lever in cockpit, just a power lever and small fuel on/off lever.
So how does it determine the prop RPM? Does it simply maintain constant RPM at all times, or is there some predefined schedule depending on power setting and airspeed, and if yes, what?

You effectively have a two speed prop (kinda like the 2 speed Power Glide automatic transmission on my first car, a 1964 Pontiac - well, not really).  It's controlled by software, and there is a 1700 rpm high rpm and 1550 rpm low rpm mode, and that's it.
The PC-12's PT-6's FADEC system controls the prop governor, which runs the prop at 1700 rpm for all settings by default. When you want to quiet things down, you push a button that engages a low rpm mode, where it runs the prop at 1550 rpm for all settings below Take Off power (if you are in low rpm mode and push the lever balls-to-the-wall, it automatically brings the prop up to 1700).
So, you take off, and the prop is at 1700.  Come back to Max Continuous, it stays at 1700, come back more for cruise, and it still stays at 1700.  Then when you want to slow it down, you push the PROP LOW SPEED switch/light just ahead of the power lever, and it drops to 1550 for all power settings, except if you go back to full power, where it runs back up to 1700.

Another innovation is a low, 1,550-rpm propeller setting. Down on the center pedestal is a push-button for shuttling between the electronic propeller governor’s normal, 1,700 propeller rpm and a lower, 1,550-rpm mode for a quieter cabin. Except for take-off—when the FADEC will automatically command 1,700 rpm—you can use low-speed mode at any time. In cruise, Pilatus says that the penalty is a paltry one to two knots.

(AOPA PILOT Article - PC-12 NGX)

Really good answer, qq from me, do you lose airspeeed in the lower RPM? How much?


text:
How much time is a commercial aircraft (e.g. A320 / B737NG families) flown manually?
FMS/FMGS computers can fly many modern aircraft between waypoints set by the crew. They find their way using aids like IRS, GPS, DME, and ILS and are able to manage route, altitude and thrust.

Mode control panel (MCP) on a B737 NG (probable source: Alessio Meneghetti on Flickr)
Most of a commercial flight can be handled by computers when everything goes as planned, air regulations don't seem to forbid such automation.
On the other hand the crew ensures flight safety, programs, engages and monitors computers, handles changes, hitches and abnormal situations, takes decisions and re-programs computers with new instructions. Some configuration changes (e.g. landing gears) are also beyond computer reach.
I'm curious to know which actions are manual and how much time is spent for them from entering the takeoff runway to leaving the landing runway, e.g. for a 2,500 NM commercial flight? What is the current trend for airlines policies regarding the use of these automation capabilities?

Your heading asks about the aircraft being flown manually but the question asks about "important actions." Are you asking about hands on yoke or are you asking about actions required while ap is on?

@TomMcW: I've added an example in the question. I'm trying to understand which part of the flight is basically flown automatically (with some inputs from the crew), and which part is flown manually (and how much time this takes).

Today's aircraft automation is just not set up for unattended operation.
There are too many individual tasks, that pilots must complete, to list here. The lowest workload for pilots is during cruise but even then ATC can instruct you to change speed, routing, or altitudes. Maybe one day this could be controlled from the ground but today only the pilots can make those changes.
I think you want to know how many minutes of an average flight are the pilots actually manipulating the controls either manually or through the A/P.

The A/P comes on somewhere between 30 seconds and 7 mins after takeoff and it stays on continually for the whole flight until maybe 2 mins before touchdown.
Every flight is different and sometimes there is lots of vectoring by ATC on departure/arrival and lots of step climb/descents, which requires the crew to "fly" the A/P. Sometimes the arrival/departure are linked up directly with the en route portion and you get a direct climb/descent.
So as a rough guess on an average flight the pilots might manually fly the aircraft for about 3–10 minutes and "fly" the A/P for about 5–10 mins. The rest of the time is spent talking to ATC, doing checklists, checking weather, fuel checks, and trying to keep yourself busy any other way you can think of. :)
I personally fly mostly ultra long haul flights of 13–15 hours as part of a 4-man crew so I also spend about 6–7 hours sleeping in the bunk.

In every phase of flight the crew is needed to do much more than just monitor the automation. The automation can not be used unless the pilots first enter all the required parameters, and then activate the automation at the right time, and in the correct order.
There is no aircraft that can take off on autopilot. The autopilot can only be engaged after takeoff. Once airborne at cruising altitude the aircraft could follow a programmed flight routing but any change in heading, routing or altitude must be manually entered by the pilot.
At the destination the approach must be manually programmed for the approach and runway in use. Once the aircraft in on the ILS approach an aircraft with autoland capability can land itself but it still needs the pilots to clear the runway.
Autopilot/autothrottle policies can vary with each airline. Typically airline pilots hand fly from takeoff to at least 200' but many hand fly to 10,000' or more for practice. When landing most pilots hand fly from about 1,000'.
Depending on the specific aircraft, autothrottle is usually engaged during the the takeoff roll and stays on until the flare just as it lands. There is no automation for landing gear and flap operation. It is 100% manual.

I added more info, but here are too many individual steps to list here. This similar question and answer has more info as well but still does not cover everything a pilot does in order to complete a flight.   http://aviation.stackexchange.com/questions/2866/on-modern-commercial-airliners-how-much-of-the-flight-could-be-fully-taken-care?rq=1

I guess I still don't understand your question, or the point of your question.  Today's aircraft can not be flown "automatically" without a pilot. What more do you want to know?

I would like to have an estimate of the effort done by the crew, when using all automation allowed (or recommended) by the airline. For example: ... and during cruise, the A/P is engaged, from time to time the crew will allow a step climb (one per hour), this is a matter of turning a knob, and takes 20 seconds..... I guess it's not so simple, but it would allow to understand the A/P could pilot and navigate during several hours, with small interventions from the crew (if this is the case indeed).

Generally all airline pilots use all the automation that is available to them. Those "small interventions" you mention require experience and decision making skills. Even just turning a knob or pressing a button to change an altitude has to be carefully considered because that change of altitude may not be safe, fuel efficient or comfortable.

Indeed Mike, I agree 110%, but that's not my point in this question.

Does the 777 have any kind of autotrim feature? At TOD do you have to retrim the aircraft or does the autopilot do all of that?

The B777 A/P maintains stab trim but rudder trim must be manually adjusted so that the roll spoilers are not activated and cause additional drag.

What about autoland? https://en.wikipedia.org/wiki/Autoland

A paper from Duke University, Functional Requirements for Onboard Intelligent Automation in Single Pilot Operations, based on interviews with commercial airline pilots, states the following:

Pilots flying the 777 agreed that they spent about 7 minutes for a typical flight actually "flying" the  aircraft,  meaning  touching  the  controls. The Airbus pilots stated they "flew" their aircraft about half that time.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What are the visual differences between the ATR42 and the ATR72?
I tried to find the visual differences between the ATR42 and the ATR72. I downloaded some images from Google but I can't find any. Would you help me?

Isn't the fuselage length not different enough between the two?

By Julien.scavini (Own work) [CC BY-SA 3.0], via Wikimedia Commons
The ATR72 is quite a bit longer than the ATR42, and has several more windows to allow for more passengers.
According to Wikipedia:

The ATR 72 was developed from the ATR 42 in order to increase the maximum seating capacity (from 48 to 78) by stretching the fuselage by 4.5 metres (15 ft), increasing the wingspan, adding more powerful engines, and increasing fuel capacity by approximately 10 percent.

So it's longer, and has larger wingspan. The stronger engines and larger fuel tanks can't be seen from the outside.

Could you add a couple of pictures? It would really help to make the point about the fuselage and windows clearer.

TL;DR Count the windows behind the wing; it's about 3 for ATR42 and 7 for ATR72.

There are a lot of technical differences between the two aircrafts. In addition to fuselage length and wing span, like ATR 72 has three cameras in forward cargo area and near cockpit door + its display screens inside cockpit, antennas outside the fugelage are different, ATR 72 navigation lights are LEDs, where as ATR 42 nav lights are normal bulbs. Similarly the cabin lights of 72 are all LEDs. The flap position indicators are different, The quantity of emergency equipment are different. The most important of all, The both aircraft have the same identical engine. ATR 72 has long fuselage but in most of the countries, it is not flown with full capacity in mountainous territories as its engine power not suitable for high rate of climb with full capacity load so no use of large fuselage.

The question asked for "visual" differences. Things like cameras in the cargo bay, cockpit displays and interior lighting really aren't "visual"/"plane spotter" differences. [Edit]ing out those items would improve this answer.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Can I get refractive eye surgery and pass a medical in Europe fitting EASA requirements?
I would like to attend a Class I pilot Licence, but my eyes are not 'the best'. If I'd undergo refractive surgery (RS from now on), and the intervention goes well, will I fit the requirements?
For example, your defect can't be more than -5 of miopy per eye before the RS.
My question mainly refers to the eligibility requirements in Europe, they seem not matching with Italian ones.
this is the abstract.
“Applicants who have had refractive surgery and are being considered for
medical certification (first time?) or recertification (this should be the second visit on) should meet the following criteria:
a) The surgery is uncomplicated.
b) Vision is stable.
c) There is no corneal haze and no complaints of glare, halos or “ghosting”.
d) The result meets the visual requirements of Annex 1, and the assessment
must be based on measurements made by a qualified vision care specialist
acceptable to the Licensing Authority.
e) There should be follow-up examinations by a qualified vision care specialist
six months after return to duty and yearly thereafter.”
If i can skip the limit of eye sight taking a licence out of Italy (for ex.in other European countries,the US, etc) will I be able to pass the EASA medical visit as a pilot qualified in the States and be able to choose where to work?
Thank you for your answers.

Answering this question for "all over the world" is pretty much impossible: You will need to narrow the scope to the one specific jurisdiction you are looking to train in. Every nation has its own regulatory structure, and its own medical requirements. Many allow you to get a pilot's license after refractive surgery, or using corrective lenses (the FAA permits it, for example. Some may not.

Welcome to the site!  This question is much too broad to be answered, because a complete answer would have to include every country in the world.  Please edit the question to include a specific jurisdiction (if you are interested in a few, please post them as different questions) and we will be able to help you out.  I would suggest that you ask it for the country in which you will apply for the medical, or for ICAO requirements, as they would be the most appropriate.

voretaq7 and Lnafziger, first of all thank you for your answers.
My question was made to understand what happens
IF i match the requirements, for example, in the US by FAA, and get the class 1 eligibility. So could I attend the training course there and become a commercial pilot, and then, as a question, move to a company of another country?

CASA (Australia): Designated Aviation Medical Examiner's Handbook /// US: Dear Capt Lim

I edited the question to focus on the EASA and Italy requirements. Feel free to improve or roll back the edits if this doesn't match your question well.

WOW in Australia even Monocular pilots are allowed in some cases o.o

@Yoda Generally speaking, medical certification does NOT transfer between jurisdictions, unlike the licence itself.

Ben the thing is: i get the licence in the States, then to convalidate it with EASA they ll surely check if i had or not refractive surgery. So won t I fit their requirements?

I find your question a bit unclear. You asked if you can get a Class 1 EASA medical after RS, but you also answered that yourself with the quote you gave. And I don't understand the final part about getting an EASA medical as a US pilot? If you aren't sure how to ask your question then you could join the chat room and ask for some help there.

Hi Pondlife, the question -and answers- might look unclear because they were edited few times. I found my answers,not in Easa website but in the different countries' regulations. The UK,for example allow you to have done eye surgery and then to pass the visit. My question about US was made to understand the validations all over the world.

Yes,
Please consult with the FAA or your governing body on flight physical requirements as well as your eye care provider about approved corrective surgeries as well as limitations.  It does take a little paperwork but should not be a problem.

Thanks Carlo, I am in front of the pc searching as hell, and I think you answered properly to my question.
I think your answer was like 'becoming a pilot 'all over the world' is now possible with eye surgery'.
I'll search deeply for my answers and if I find something I'll post the results here.


text:
How much does it cost extra to fly with one additional passenger?
How much does it cost to fly an airplane (like a Boeing or Airbus) when  there's one extra passenger there, at an average speed of 475–500 knots (880–926 km/h; 547–575 mph)? That is, about 100kg extra, including clothes and luggage.

for 1 minute or 10 hours?

What you are asking is essentially the payload's marginal cost, but as Federico says you need to add a denominator, like time or range.

OK, at an average speed of 475–500 knots (880–926 km/h; 547–575 mph).

that does not answer my question. we asked for either a distance or a duration. a speed is neither.

Surely it's possible to give an answer of the form "it costs an additional $X per hour"? I don't see any need for the asker to specify an amount of time.

@TannerSwett but then the question needs to be phrased in that way. I previously had plenty of discussions with people saying that the way I answered was "wrong" because they interpreted the question differently. So now I am not even attempting an answer if there is a remote chance of that occourring again.

@TannerSwett moreover that question could not be answered, since the fuel consuption is not uniformly distributed over the flight, but concentrated on takeoff. so a short flight has a larger cost increase "per hour" than a long one.

@Federico That's a good point.

Possible duplicate of How much of an improvement would a 1% weight decrease on an airplane be to the industry?

@Federico Would computing the answer giving fuel burn for TO, then cruise per hour make it too complicated for you? Is that what you’re saying?

@Koyovis are you saying you can be sure that would answer the question?

@Federico I reckon it would, then if not I'd listen to the comments and incorporate in the answer if reasonable.

@Koyovis ok, then feel free to go ahead. I don't have much time to write an essay on fuel consumption.

Not a duplicate. This question is about payload, the referenced question about empty weight reduction.

Related question of Physics.SE

I am basing the following calculations on the excellent answer by Peter Kämpf to this question: How much of an improvement would a 1% weight decrease on an airplane be to the industry?.
We can approximate the fuel usage with the Breguet equation
$$ m_\mathrm{TO} = m_\mathrm{Landing} \cdot \exp \left( \frac{R \cdot g \cdot b_f}{v \cdot L/D} \right) , $$
where:

$m_\mathrm{TO}$ is the total mass at takeoff
$m_\mathrm{Landing}$ is the total mass at landing
$R$ is the distance flown
$b_f = 0.000018 \mathrm{kg} / \mathrm{Ns}$ is the fuel burn
$v=250 \mathrm{m}/\mathrm{s}$ (about 900 km/h) is the velocity
$L/D=18$ is the lift to drag ratio

Assuming a fully loaded A320 (OEW $ = 42.6 \, \mathrm{t}$ with $ 19.9 \, \mathrm{t}$ payload and $3 \, \mathrm{t}$ reserve fuel $\Rightarrow m_\mathrm{Landing} = 65.5 \, \mathrm{t}$), we can do the calculation for the fuel ($m_\mathrm{TO} - m_\mathrm{Landing}$) with and without an extra 100 kg and compare for different distances $R$:

Note: this equation become increasingly inaccurate towards small distances because the takeoff, which uses more fuel, is not taken into account here.
Using the given speed, this can be converted to different flight times:

And by multiplying with the current jet fuel price of 616 US Dollars per metric ton, we get the additional cost of a 100 kg passenger per flight time:

I did similar calculations based on the other answer to the cited question (B747-400; 12,700 km, 400 t MTOW, 175 t fuel) and ended up with a plus of 43.75 kg fuel for 100 kg of extra load.

If you want to take fuel use during takeoff into account, these numbers might help.

I just stumbled across this FAA document that provides details on the incremental fuel burn due to additional weight.

As noted above, incremental fuel burn related to an increase in aircraft weight was calculated for selected aircraft types and selected stage lengths. The aircraft types selected present a sampling of the most common aircraft in use within each economic values category. Mission lengths were based on typical mission lengths for each aircraft type, as observed in FY 2013 ATSBM data. For most aircraft models, multiple mission lengths were analyzed. A weight penalty of 500 pounds was used for most larger narrow-body and wide-body jet aircraft, while a weight penalty of 200 pounds was used for most smaller narrow-body, regional jet and turboprop aircraft. In a few cases, these weight penalties did not produce reliable results so a different weight penalty was used.
Table 6-1 presents the results for all large commercial aircraft (including both passenger and all-cargo aircraft). The table presents the aircraft type, passenger or cargo configuration, the stage lengths analyzed, the weight penalty and the incremental fuel burn in pounds per flight. In addition, the incremental fuel burn per pound of weight added is also calculated in U.S. gallons per flight. The incremental fuel burn in gallons per hour per pound of weight added is calculated by dividing the incremental fuel burn per flight per pound of weight added by the flight time. Also shown is the total flight time for the specific mission analyzed.

Link broken.
https://www.faa.gov/sites/faa.gov/files/regulations_policies/policy_guidance/benefit_cost/econ-value-section-6-perf-factors.pdf

This depends - among others - on the size and speed of the airplane, as well as the total trip duration. As a rule of thumb (based on fuel consumption data of a major airline), I've been working with 4 to 5% per hour of flight time (for jets). Yielding some 40 to 50 extra kgs of fuel for a trip of 10 hours, that is in accordance with the calculation done by @PerlDuck .
This answer over-simplifies stuff a lot, of course, but it's a bit easier for back-of-the-envelope calculations.


text:
In what order were the runways built at Paris Charles de Gaulle?
At its commission time (in 1974), Roissy-CDG airport did not have all its runways in service. As an example, I found an article (fr) saying the fourth (and last) runway was built in 2000. But this article does not precise which runway it was.
I'm curious about how the extension of this airport was handled. Wikipedia gives an overview of terminal  extension history but not of runway.
I imagine the first runway to be commissioned is the 09L/27L as it is the nearest to the first terminal, but then, what happened? Was the 09R/27R commissioned before the southernmost runways? Did they built a runway on the south before building the smaller outer runways? In short, in what order did they build the runways?
Bonus question: Did they already have changed the runway names?

Related: What did Paris' de Gaulle airport look like before the t2 expansion?

Overview

(background image: Wikimedia)
Details
The first runway was finished in 1971 as 09/27 and it corresponds to todays 09R/27L:

Work on the satellites started in late 1970. Also built were Air France and UTA hangars and a pooled cargo terminal.
  Construction on the first 11.800-foot (3,600-meter) runway, 09/28, and its associated taxiways started on August 1st, 1969.
The runway was inaugurated by the Ministry of Transport on September 9th, 1971. The earthworks of Runway 2 were started in 1972.

(airporthistory.org)
The second runway was finished in 1976 as 10/28 and corresponds to todays 08L/26R:

In 1976, Charles de Gaulle handled 7.5 million passengers and opened a second runway. Initially, the second runway was built at a reduced length of
  9.400 feet (2,900 meter) and without a parallel taxiway. It was only used as a backup when the main runway was inoperative or at the instruction of air
  traffic control. The runway could be built out to its full length of 11,800 feet (3,600 meters) and taxiways added when traffic demand required.

(airporthistory.org)
The following ground chart shows the layout in 1977:

(image source: flickr.com by jwhshd)
By 1994, the terminals had been greatly expanded to the south and the new runway was at its full length (I don't know when exactly the expansion happened):

(image source: flickr.com by jwhshd)
The third runway was finished in 1999:

Expansion of Paris Charles de Gaulle (CDG) Airport has also helped Air France. A third runway at CDG opened in 1999, with a fourth to open in 2002.

(Strategic Management in Aviation: Critical Essays)
Unfortunately, the source does not detail which runway this was. By searching through pictures of CDG from 1999 on airliners.net, I was able to find the following quotes:

Landing on runway 26L

(airliners.net, May 1999)

Taxiing out runway 27

(airliners.net, May 1999)
This would suggest that the runway numbering had already changed and the second runway to the south (08R/26L) was built first (in 1999). This would leave runway 09L/27R to be the fourth runway added in the early 2000s.

Wonderful answer

The ICAO ID of Roissy is LFPG (not LFGB as indicated on the Wikimedia drawing, LFGB is Mulhouse). Well researched anyway.


text:
How does the traffic pattern at a large airport affect nearby, smaller airports?
Do the landing and takeoff directions for a smaller airport (GA and bizjet traffic) change when the traffic direction at a nearby large airport changes?
Specifically, I'm wondering about how traffic at FTY and PDK would be affected by the direction of traffic to/from ATL.

Generally speaking when airports like this are close together the airspace is designed to allow operations at both airports to occur without interfering with each other.
Broadly speaking if one airport changes approach direction it may be the result of a wind change. Assuming the local prevailing winds shifted its likely the other airport will change approach direction as well due to the wind shift.
The VFR sectional actually sheds some light on your specific area in question

(source)
In other words, if your flying VFR its likely that IFR aircraft from the outer airfields will initial be assigned to 3000 ft. (so keep your eyes on the lookout) and if we look at the Class B floors around that area 3000 keeps you under them in most places. In a round about way you can infer that controllers are going to assign and vector you under the class B to keep you out of the ATL area. Runway turnarounds or not.

The floor of the ATL Class B airspace over Fulton is 3500 ft all the way south to the edge of the Fulton control zone so I'd say there is no impact at all for aircraft coming and going from FTY/PDK in terms of runways or traffic patterns close to the airport.


text:
What is the linkage connecting the body landing gear on the C-130?
I can't seem to find a diagram that includes this tube linking the front and rear body gear on each side. Is it structural, or hydraulic, or maybe something else entirely?

Image source: https://www.airport-data.com/aircraft/photo/001380858.html
Additional photo: https://www.airport-data.com/aircraft/photo/001454050.html

It's structural. It's called a truck assembly or a bogey, on most aircraft. I used to work on C-130s, but it's been a long time and I don't recall the exact nomenclature that is used for that part in the C-130 world anymore. But it's just a structural part that keeps the front and rear wheels aligned with each other. Each main gear axle has a shock strut that retracts and extends on a jackscrew. Without it, there would be a lot more twisting force on the landing gear parts, which would lead to premature wear and potentional emergency situations that you definitely don't want to experience when taking off or landing. That part absorbs some of the twisting force and lightens the torsional load on the gear itself.


text:
Do any aircraft automatically test that the pitot-static system is functioning properly before liftoff?
Given that a properly-functioning pitot-static system is absolutely essential for flight (a plane cannot be flown without valid airspeed data, or at least not for long), are there aircraft that automatically check the functioning of the pitot-static system before liftoff?  This seems like it would be quite easy to do; during takeoff, compare the airspeed measured by the pitot-static system against the groundspeed (which could be read from speed transducers mounted on the landing gear), and sound an alarm (“INVALID AIRSPEED” or something similar) if the rates of change of the two fail to match within a certain tolerance (indicating either a failure of the pitot-static system or severe windshear along the length of the runway, both of which necessitate rejecting the takeoff).

Also Is it possible to detect a pitot static failure (blockage) of air data probe during flight and alert the pilot? and  How can a pitot tube freeze when it's heated?

I've tagged your question "airliner" because I'm assuming that's what your interest is. Transducers sound like an unlikely feature on the landing gear of a Piper Cub, for example :-) If that isn't your intention, please just just roll back or edit as you like.

First of all, ground speed is already determined by the IRU’s. No need for landing gear sensors although most airplanes do have WHEEL SPEED transducers for anti-skid currently installed. Wheel speed is not always equal to groundspeed but can be at times. For example, wheel speed right after takeoff is different than ground speed because the wheel begins slowing the second it leaves the ground.
Second, airspeed changes with altitude. So, the higher you are the faster your airspeed. This means that taking off in Death Valley might show a different airspeed RELATIVE to groundspeed than in La Paz El Alto.
Third, most of the time, airspeed doesn’t register correctly until about 60 knots. You’ll see that most airspeed indicators have 60 knots as the lowest indication mark. This is because if the airplane is pointed into the wind, it could register spurious readings. So, before any checking gets done, the plane needs to be moving above 60 knots.... Like during takeoff.
Fourth, airspeeds are cross checked during takeoff roll. The vast majority of airspeed splits on a new flight leg occur on takeoff roll and result in a rejected takeoff - your premise anyway. Occasionally it’s not noticed until takeoff. This is rare. The other instances (which I work on more frequently) are in flight malfunctions usually related to inadequate pitot heating.
Fifth, the current system works very well. No need to reinvent the wheel.

Comparing it to ground speed won’t work. If there’s any wind the two won’t match.
On airliners there are multiple pitot systems. Usually one displayed to the captain and one to the first officer and often a backup. Failures are detected either by the aircraft systems or the pilots themselves cross checking their readings for a mismatch.

Hence why I suggested comparing the rates of change of the airspeed and groundspeed, rather than the speeds themselves.  They should both change at approximately the same rate if the pitot-static system is functioning properly and the amount of headwind isn't wildly changing.

but windspeed is usually measured by comparing airspeed and ground speed, you'd need new equipment to measure wind speed to filter out the gusts


text:
Is there still a minimum height required for becoming a Lufthansa pilot?
basically what the title says. Do I still need to be at least 165 cm to become a pilot or has this changed? There is no limit stated at their website but they also don't tell you that there is no limit.

Hello Sophia, welcome to aviation.stackexchange.com!

Wow, a 50th percentile European/North American female is 162 cm (5' 4"), Lufthansa is basically disqualifying half of all women automatically.

This page for pilot applications shows a 165cm number.
I didn't translate to see what it's for
https://career.be-lufthansa.com/index.php?ac=search_result&search_criterion_activity_level=107
4 pilot jobs listed, only the first 3 show the 165cm.

Can confirm that those 3 are requirements to be taller than 165cm. The 4th is a posting to train as a pilot, no guarantee to be employed as one later (but one would assume good chances if you manage to get in the class)


text:
Can I apply for ASEL and Glider class ratings at the same time?
I would like to get both FAA Private ASEL and Private Glider class ratings.  I was told I could take lessons for both ASEL and Glider at the same time under a Student certificate.
Can I apply for a Private certificate with ASEL and Glider ratings at the same time? And is it more beneficial to do this than to get ASEL first then Glider?

Which jurisdiction?

You "apply" for a rating or certificate by showing up at the examiner with proof of your written test and taking a flight test -- so of course you can only do one at a time! But I think you want to know if you can train for both airplanes and gliders at the same time, under the authority of the same student pilot certificate. Yes you can do that.
However I do not recommend it. They are very similar of course, but there are enough differences that while you're learning to fly, you should just pick one and get your certificate. Then learn the other.
If you want to fly both airplanes and gliders, there is no particular order that is better than the other. I fly both airplanes and gliders; I happened to do airplanes first because there was no convenient glider field close to where I lived at the time. Now I fly both and I feel they complement each other and it's great!
But while you're learning, pick one and get it done; then do the other one.
(This may only be correct with the FAA in the US. And to be fully FAA-pedantic, Airplane and Glider are "categories"; "single-engine land" is a "class" that is available in the Airplane category. Thus ASEL is category-and-class, but Glider is just category.)


text:
How can a flying wing style airplane recover from a spin without a vertical stabilizer?
I fly a Cessna C-172, and if I have any bank when stalling, I have to use rudder to level the airplane. If I use aileron, the bank angle will increase and bring the airplane into a spin.
My question is, if there is no rudder or vertical stabilizer, like a B-2 bomber for example, how could a plane recover from a stall?
This question is different from others because this is not focus on the stability or control of 6 freedom. I would like more discussion on the recovery of spin and stall.

Stall Recovery
Similar to the vertical tail on your Cessna, a flying wing produces only little lift or even a downforce over the rear part of its wing. A swept flying wing uses washout for the same effect. In all cases, the idea is to produce relatively more lift increase with an angle of attack increase in the rear parts of the wing (or the tail in conventional configurations) so the aircraft stabilizes itself.
This also means that the center of lift is ahead of the quarter chord point of the wing, and the same goes for the center of mass. At high angle of attack you need to create a pitch-up moment with the elevons in order to trim the high angle, and once the wing stalls, this pitch-up moment is reduced. As a consequence, the flying wing will pitch down and recover. Again, this is very similar to what happens on your Cessna, only that the function of the tail is performed by the rear part of the wing.
Wing sweep helps a lot to pull the aircraft into the wind, and the yaw inertia of the big wing helps to keep rate changes down. Stalling in banking flight produces a very similar reaction as a straight and level stall while the airplane continues to turn. Of course, pulling too hard and preventing the wing from correcting the high angle of attack itself will risk to force the flying wing into a spin.
Spin Recovery
Flying wings have only a steep spin mode. Flat spins are not possible because the flying wing lacks the lengthwise mass distribution of conventional airplanes which creates a strong pitch-up moment in a spin. If the flying wing has no fuselage protruding in front, it also lacks the stabilizing nose vortices which are a contributing factor for flat spins.
Spinning the SB-13 was quite harrowing: The nose points almost straight down and the aircraft loses about 100 m in one turn. But ending the spin was simple: Just pitch down and stop the rolling motion by allowing the roll damping of the wing to kick in.

The answer depends on the type of flying wing aircraft.
Drag rudders
The B2 for example is an example of a flying wing aircraft with rudders. It's just that it doesn't use conventional boat style rudders attached to vertical stabilisers since it doesn't have any vertical stabilisers. Instead it uses drag rudders.
There are several different types of drag rudders. The B2 uses one of the most effective designs as proven by countless experiments: the split elevon (sometimes called duckerons since they look sort of like duck bills). If you look at pictures of B2 landing you can clearly see them open at the wingtips.
Regardless of the type of drag rudders, they work via 2 principles:

The simple to understand one whereby if you increase the drag on one wing you make it advance slower than the other wing thus inducing a yaw.
The less obvious principle of shifting the center of drag backwards. This is the same principle of how badminton shuttlecocks work. Indeed, this is the same principle of how vertical stabilizers work. If the center of gravity is in front of the center of drag you get a weathervaning effect where the draggy part would swivel to the rear. The B2 achieves this by opening both drag rudders. In effect the B2 is creating a less efficient, more draggy, virtual vertical stabilizer. In practice you'd only need this extra stability when flying slow. At cruise speeds the drag rudders would be mostly closed (especially if you have them gyro stabilized, if you don't have computer controls and gyros you'd keep them partially open for stability).

Wing twist/washout
Some flying wings don't have drag rudders. Instead the wing is twisted to achieve a lift distribution that would cause the wing to have proverse yaw. The Dunne series of flying wings were promoted as inherently stable aircraft because they didn't experience adverse yaw. If you have proverse yaw you can simply use your ailerons to turn the plane without rudders.
The big disadvantage designs that don't use drag rudders or any vertical stabilizers is that you depend on banking in order to yaw. This makes landing on straight runways impractical so most such planes land on grass fields which allows the pilot to choose landing direction so that crosswind is not an issue. A lot of Dunne flying wings were seaplanes.


text:
What is auto-rotation?
Inspired by this question.
My knowledge concerning helicopters is quite limited:

what is auto-rotation?
are there other "rotations" possible?
in what do they differ?

http://en.wikipedia.org/wiki/Autorotation

the "duplicate" question, while ultimately ending at the same answer, is nowhere near the same question.

When a helicopter engine fails, the pilot lets the rotor blade rotate freely pushed by the wind as the helicopter is falling out of the sky. This is called auto-rotation.
Normal rotation is with the engine powering the rotor.
The most important goal of auto-rotation is to get enough lift right before touch down by flaring so the landing is not a crash.
You would also enter into autorotation when the tail rotor becomes ineffective and you can't recover it otherwise.  Once the tail rotor is back into action you can drive the rotor again.

so the crash isn't as bad - what leads you to believe that autorotation leads to a crash?  I've done many autorotations and have not crashed yet!

I'll be more direct.  A properly execute auto results in a perfectly controlled, safe touch down.  isn't as bad means nothing ;)

@Simon if you know so much why not make your own answer :)

@Simon how many autos have you done to a full touchdown? I'd guess not many as in training they're usually only executed to the flare and then power is rolled back in. That extra couple feet is a big deal... PPL training goals are to survive the landing, not to grease the touchdown.

@dvnrrs  I've never counted but I guess about 15.  I trained before JAR.

@ratchetfreak  why not make your own answer because you've pretty much summed it up.  I just took exception to the "crash" assertion.  The point I was trying to make, and encouraging you to edit your answer, is that in many types, autos are almost no-events.  A bit frisky in low interia types but quite relaxed affairs in something like a 206.

@dvnrrs  I should also add, always run ons and always to grass. I'm not good enough for zero zero.

@Simon No shame in that. It is not an easy maneuver all things considered!


text:
Single engine failure in a light twin after lift-off: what to do?
In a previous question the case about if a turnback would be feasible, specifically for a single engine aircraft, has been analysed.
But given a twin-engine general aviation aircraft and a single engine failure immediately after lift-off, considering that my Pilot handbook says:

A continued take-off is not recommended if the steady rate of climb according to "Section XX" is less than Y%.

Considering the quite dangerous setting, I would say that is quite impractical to go and check that table in such a situation.
What kind of indicators might I look for to check if it safe to continue? Should I learn by heart such table? (I am not sure this is practical either, is a quite complex table)
In case I am unsure what to do, apart from trying to climb for a while then turn around or immediately try land in front of me (granted that there is enough space), are there, generally speaking, other options?
In the accepted answer of the listed question is said that

It's not reasonable to try it [a turnaround] without knowing what altitude is needed for it at current conditions.

is it possible to estimate this quickly inside the cockpit?

point is with a single engine a plane should be able to maintain level flight which allows for more freedom than with no engines

@ratchetfreak that is what I thought, but that sentence in the POH made me think.

Doesn't the "Section XX" have a table from which you can get the "Y" during preflight?

@ratchetfreak: IIRC the rules only apply to transport category aircraft, but not general aviation.

@JanHudec That's the exact point that I was going to make.  You should look this up before every takeoff, just in case you need it!

What you really should learn by heart is the flight speed for best climb with one engine inoperative. Try to trim that immediately and you will win more time to make a decision. The rest is really depending on circumstances: Is there a landing opportunity ahead? Are you high enough to do a 180 and land on the same runway in opposite direction? Or are you high enough (and the aircraft does not lose altitude) that you can fly a pattern and land normally?
Testing the aircraft at altitude with one engine throttled is highly recommended, but be aware that the remaining thrust / drag of the throttled engine might be different from that of the stopped engine.

I believe if the propeller can be feathered, the difference will be reasonably small.

@Jan Hudec: You are correct. But if you do not have much altitude and there is plenty to do in the cockpit, pressing the prop pitch switch long enough will not be first priority. Always plan for some non-optimal condition.

@PeterKampf i havent touched a multi piston prop in 9 years and i still have the "mixture, prop, throttle, dead foot dead engine, verify throttle, prop feather, mixture cutoff" muscle memory.

After you've learned your airplane and its characteristics, you will know if something is not right. The decision to land, when that's something that can be safely done, is never the wrong one if you're not comfortable with your performance and problems can be checked out on the ground with nobody dying usually!
Regarding a safe altitude to turn around in... you need to know your aircraft to answer this, but it's not terribly difficult to learn. You can fly to a few thousand feet AGL (preferably with a CFI or other capable safety pilot), fly at whatever speed you climb at, pull your throttle out and see how much altitude you lose while doing a 180 degree turn (simulating turning back to your departure runway). Try this under different conditions (max gross weight vs. generally empty; high density altitude vs low for example) to learn how these factors affect your altitude loss. Then apply a safety margin.
I've been taught that a general figure (without recognition of the specific aircraft or conditions) is 500 feet. This is not to say a turn-around is safe at 500 feet! It's just a baseline of consideration. Other factors are going to include how much runway you're going to have if you're able to turn around!
One of my primary instructors, before every first launch of the day, had me go through an aborted landing briefing similar to: if we have an emergency below 500 feet we're going to land straight ahead. Below 700 feet, we're going to turn to the (left/right) and land on the crossing runway (my airport had 9/27 and 5/23). Higher and we will turn left/right and land on the parallel runway (9/27 R/L; easier to get to than a full 180 in-place).

You are more likely to kill yourself in a stall/spin trying to turn back than you are from a forced landing straight ahead.
Since the altitude required to make a successful 180 turn is quite considerable the chances are if you are high enough you will be too far from the runway to make it back.
I remember seeing an article in plane and pilot magazine back in 1974 dealing with that topic and I seem to recall anything below 780ft AGL was a no-go

If your angle of climb is better than gliding angle, at higher altitude you will be more likely to make it back. If it isn't, you won't, ever. Also beware that the minimum altitude depends very much on the aircraft and the weather, because density altitude affects rate of climb quite significantly.


text:
Does a dual-rotor helicoptor like the Chinook transition from hover to forward flight differently than a single rotor helicopter?
I watched this video of an RAF Chinook taking off vertically and transitioning to forward flight.
I'm curious if the method for increasing lift to move forward, controlled by the cyclic in a single rotor if I'm not mistaken, is different when you have two rotors along the length of the aircraft. My untrained assumption is that to lift the rear of the helicopter and start moving forward, you would increase power or the collective on only the rear rotor.

May just be pitch changes on both rotors

First
-collective variation = intensity
-cyclic variation = direction
The CH-47 Chinook is a heavy maneuver and assault helicopter manufactured by Boeing. Its two tandem rotors (set of horizontal rotors mounted one in front of the other) are counter-rotating and are controlled synchronously in stationary and in translation, thus their torque effect is canceled out by their opposite direction of rotation. It is equipped with two turboshaft engines with a power of 2,850 hp to 3,750 hp,(help to moving forward) with a maximum weight of 18.5 tonnes.
Photo below we see that the rear rotor is raised relative to the front rotor.

an asymmetry of the lift between the 2 rotors implies a tilting along
  its pitch axis and causes the device in forward flight.the tandem
  rotors are very bulky and not very maneuverable, which constitutes
  their main defect. Note also that the lengthening of the fuselage
  makes them more sensitive to strong wind

So it's mostly like an helicopter with one rotor( cyclic variation to move forward) but a few different.your hypothesis is not really right because the two rotor are connected and
are controlled synchronously in stationary and in translation(same speed)
The main MGB gearbox is interconnected with the shafts of the two turbine engines. A seven-section shaft connects the main gearbox to the front gearbox, and a two-section shaft connects the main gearbox to the rear gearbox. The oil cooling fan is driven by the rear gearbox.
Source:https://www.google.com/url?sa=t&source=web&rct=j&url=https://tel.archives-ouvertes.fr/tel-00709015/document&ved=2ahUKEwjH3qT05droAhVM4YUKHfc5DtAQFjAEegQIBhAC&usg=AOvVaw1SPfruh9nYtNK5IvBNd6v4&cshid=1586416929818
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.lavionnaire.fr/HelicoAnticouple.php&ved=2ahUKEwjH3qT05droAhVM4YUKHfc5DtAQFjAGegQIARAB&usg=AOvVaw1YZG69MlCkIC6sLwiWFvb8&cshid=1586416929818
Longitudinal control of tandem rotor helicopters is accomplished by differential thrust of the forward and aft rotors creating pitch attitude changes of the fuselage about its lateral axis.
Lateral control is accomplished by the lateral tilt of both rotor discs, which causes the fuselage to roll about its longitudinal axis

Directional control is accomplished by differential lateral tilting of both rotor discs, which causes the aircraft to turn about its vertical axis.

Helicopters don't tilt the rotor. The cyclic control varies lift of blades in different positions, which shifts the centre of lift sideways. Since the blades are free to flap up and down, the plane of rotation does tilt a little, but that is an effect, not mechanism, and the shaft does not.

Wrong:
The pilot has three commands:
The lifter manipulated by the feet which controls the yaw axis, i.e. the pitch of the anti-torque rotor
The broom or cyclic handle which controls the axes of pitch and roll
Finally the general or collective pitch located to the left of the pilot who controls the engine and the pitch of the blades. Flight controls and their actions The principle of anti torque.

For the cyclic the tray is tilted!

https://www.lavionnaire.fr/SiteImgHelico/RotorPlatCyclique.png

That image is wrong! It correctly shows the swash-plate (indicated by the dotted red arrows), but not it's effect. It does not tilt the rotor head. Rather the scissor links change pitch of the blades. Both cyclic and collective work (on single-rotor helicopter) by moving the same swash-plate. Collective moves it up or down as a whole, cyclic tilts it. For correct explanation, refer to wikipedia.

Now of course in tandem-rotor helicopter the pilot has the same controls, but they are connected differently, since forward pitch command instead of tilting both swash plates forward instead raises the aft and lowers the forward, while side pitch still works by tilting both swash plates sideways. But the rotor heads don't tilt; the blades change pitch—and flap somewhat, so the plane of rotation does change, but as a secondary effect due to the helicopter lagging behind the rotor.

I dont say contrary that collectif=up/down and cyclic inclined!

i am ok with you


text:
Why do some T-tail aircraft have a protrusion on the top front of the tail?
Aircraft like the Tu-154 and VC-10 have a "point" on the T-tail, while others like the 727 do not. Is this structure a shock body, or otherwise related to the tail's aerodynamics? And why is it only found on some designs?
Tu-154

VC-10

727

I am somewhat confident this was already discussed, but the search being what it is I can't find it now.

@JanHudec I had hoped I could find a post (here or elsewhere) discussing the design but I came up empty. I may be using the wrong terms to search with, though.

Related: https://aviation.stackexchange.com/questions/56900/what-is-the-aerodynamic-purpose-of-an-acorn/ https://aviation.stackexchange.com/questions/26234/what-are-the-spiky-things-on-the-back-of-the-antonov-225-vertical-stabilizers/ https://aviation.stackexchange.com/questions/22237/what-is-the-teardrop-shaped-appendage-on-the-t-6-texan/

@gszavae, the first one is basically duplicate (but now there is an answer here that's  better than the accepted one there), the second is somewhat related, the third is not related at all.

@JanHudec third answer may be interesting to people re: niels nielsen's answer.

@gszavae, but its very different. The thing on Texan is really just an antenna housing, and is much smaller. The bullet fairings are never added just for sake of housing antennas, but always to reduce interference and/or compression drag and then possibly utilized for antennas since they need to be there anyway.

@JanHudec I understand, just thought it would be an interesting example for anyone reading niels nielsen's answer, and it's another example of a bullet fairing in a more general sense.

Does this answer your question? What is the aerodynamic purpose of an Acorn?

It does! I have never encountered the term "acorn" before so I missed that post. I like John's answer on this post a bit more though, he went deeper in to the aerodynamics.

It's a "bullet fairing".  Sometimes you get the pressure fields of the vertical and horizontal surfaces in alignment so the lowest pressure zone of the vertical fin is merged with the lowest pressure zone of the horizontal tail right at the intersection of the surfaces.  It results in a more extreme pressure recovery aft and can cause flow separation and vibration, and sometimes shock wave effects at high speed.
The bullet effectively moves the pressure field of the vertical surface forward to bring it out of alignment with the one of the horizontal surface.  It's usually an add on resulting from interference issues that are discovered in the wind tunnel, or during flight testing.

In some aircraft, that protruding spike houses the high frequency comm antenna and its tuning mechanism. In others it contains parts of the elevator angle-of-attack control mechanism.

Neither is reason for adding it though. They are just uses for the space when it is available.

So, the space isn't designed on purpose, engineers just might put stuff in it "when it is available"?  (Because sometimes it is available, and other times, not?)  That doesn't make any sense...

@MichaelHall, yes, engineers just put stuff in wherever it fits. They decide on what volume and weight they want for the intended mission, then design the shape to be aerodynamically efficient and then lay out the stuff where it fits. So if they add a bullet fairing for aerodynamic reason, they'll take advantage of it to put some communication equipment there, but if not, they'll stuff it somewhere else. The antenna will probably still go in the tail, but it's not as big and the electronics will just go somewhere else, connected with suitable shielded cable.

@MichaelHall you misunderstood. That protrusion is designed for a specific purpose, but that purpose is not to actually create some space, but rather to move a pressure field. Once that solution to move a pressure field was implemented and created some space as a side-effect engineers next determined what to put into that space now that it exists.


text:
What is the source of emergency power for a 727?
I've found a couple of sources that state the 727's APU cannot be started while flying, as it draws air from the wheel well.

It drew air from inside the wheel well, so it was only for use on the ground.

https://aviation.stackexchange.com/a/37715/34744

The APU on the Boeing 727 can be used for ground operation only.

https://www.boeing-727.com/Data/systems/infoapu.html
Additionally, the battery on the 727 doesn't power all of the systems on the "essential bus", and presumably cannot start the engines.
http://cyberpilot.tripod.com/electrical_system.html
So what happens if you lose all engine power in a 727? How can the engines be restarted?

Ram air turbine?

@DavidRicherby Using a RAT to start a jet engine? Not saying you're wrong, and there is the advantage that the engine is already windmilling, but still, wouldn't that require a bit more power than those can normally deliver, especially if you're already running some systems (hydraulics?) off it?

@aCVn Dunno -- that's why I put a question mark after it.

Most engines can be windmill started above some speed.  Some have to be going a lot faster than others depending on how strong the ram effect into the compressor inlet is.  You just need power to the igniters and possibly boost pumps.

@JohnK that makes sense, I hadn't considered that you can rely on the ram air pressure since, well, you'd probably stal if you go much slower than the 150 knots mentioned by bclarkreston.

According this rather detailed page on the 727's engines:

To restart in flight, an "air start" may be attempted. The start
  switch should be placed in the FLIGHT START position which will arm
  high energy ignition. The starter valve will not open. Ram air
  entering the engine is sufficient for start if the aircraft's speed is
  above 150 knots. When the start lever is moved to IDLE, fuel is
  introduced and the igniters are activated.


text:
Who operates delivery flights for commercial airlines?
Seeing an A220 flying to Atlanta for delivery to Delta made me wonder: Which crew operates a delivery flight? The manufacturer’s pilots? Or the airline’s crew?

When I worked for Boeing as an intern in 2000, I got to see Boeing’s wide body delivery center in Everett, WA.  Back in those days at least, the airlines brought out a crew of lawyers, aircraft brokers and test pilots.   Typically what happened was the airline’s test pilots would take the new aircraft up for a check flight with Boeing’s factory test pilots.  This consisted of flying the aircraft from KPAE east to Moses Lake (KMWH) where they would shoot a couple of approaches and test the avionics and systems on the new airplane, then fly west out past KPAE over international waters where they, at least technically, “bought” the airplane.  Doing this outside the boundaries of the US allows the airlines to avoid paying 8% Washington State sales tax on a $200 million airplane.  The test flight concluded, they returned and landed at KPAE.  After that the airline’s lawyers and broker met with Boeing’s lawyers and a purchase price was agreed upon.  A phone call was made and the funds were electronically transferred from The airline’s bank accounts to an account belonging to Boeing.  After that, the airline’s test pilots flew the airplane out and put it into immediate service.  Typically if the airline had scheduled service from KSEA the airplane was flown on a short VFR hop down to SeaTac and parked at a gate, where it was immediately prepped and began passenger service.  When I was there, Aeroflot took delivery of a 777 which was flying from Seattle to Moscow the very night the airline took delivery.  Other strange things are negotiated in the purchases.  Cathay Pacific once made a deal with a WA state cherry co op along with the purchase of an 747-400F; the airplane flew back to China brand new with 20,000 lbs of bing cherries aboard!

Comments are not for extended discussion; this conversation has been moved to chat.

In the bunch of European airlines I’m familiar with, it was usually an airline crew, very rarely a third party hired crew. Since customer acceptance happened at the delivery centre (required fixes are easier there than afterwards), the transfer to the operator was completed there, too.
A comment hints at that elsewhere sometimes it’s also a manufacturer‘s crew, but I don’t know any details on circumstances affecting this.

OEM production pilots also do deliveries.  Especially overseas.

@JohnK Didn’t know that, thanks!

The inspection for acceptance by the customer quite naturally requires staff from (or representatives of) the customer, and is a serious argument for the arrangement. On a slightly less serious - and purely anecdotal - note, taking delivery of a brand new aircraft in an exciting place and flying it home along a new and interesting route is not always an unpopular job. In fact, it turns out it often requires the most senior pilots to do it - at least for small operators where taking delivery of a new aircraft is a rare occurrence.


text:
What is the working principle of gravel kits?
In this answer gravel kits are mentioned. I then looked at the wikipedia page and I noticed that they are quite different from what I was expecting:

I was expecting some kind of "shield", plate or extended inlet on the bottom side of the engine.
Wikipedia says that these instead are

vortex dissipators, using compressor bleed air

How do they work? How does a beam and a sidewise jet of air prevent FOD ingestion?

Not sure it's possible to "ingest" damage?!

@LightnessRacesinOrbit admittedly is not the most clear of acronyms. According to Boeing it stands for Debris, not Damage (for example) http://www.boeing.com/commercial/aeromagazine/aero_01/textonly/s01txt.html

@LightnessRacesinOrbit I've never heard anyone expand FOD to include "damage". It's always "Foreign Object Debris".

@egid I've only heard FOD expanded as "foreign object damage."  (USMC air wing, 1996-2001).  This despite the fact that in context it usually refers to the objects rather than the damage they cause, i.e., "FOD bag", "FOD can", "FOD walkdown".  "Foreign object debris" doesn't even make sense... it would just be "foreign objects."

Then again, if it were "damage", the common phrase "FOD damage" would be redundant.  None of it makes much sense. :)

Ahha. Yes. Foreign object debris sort of makes sense - you could also have foreign objects that weren't debris. Like birds. :)

@KevinKrumwiede yes, because I have never seen examples of RAS (Redundant Acronym Syndrome) Syndrome. Especially when entering my Personal Identification Number Number.

@egid: Seems to have been a terminology shift, possibly from before you entered the industry. Sadly, Kevin is right and the new meaning is all sorts of buggered-up in English!

Well, it's been that way since ~2000 in the stuff I've seen. It doesn't make a lot of sense to do a "FOD sweep" or to "pick up FOD" if D is for Damage. I imagine the current usage dates pretty far back and "Debris" is something of a backronym to make the usage somehow more sensical. Who knows!

@LightnessRacesinOrbit Interesting find.

Notice the path of condensation leading up from below this engine into it:

That image was taken from this video, and it clearly demonstrates that there exists a path of air which flows from ground level up into the engine. Any debris on the ground is liable to be sucked up in that vortex. The nozzle is designed to break up the flowing air on that specific, well-known path.
Note that even when there is no condensation to make the vortex visible and obvious, it still might exist.
Here is a nice intake vortex video, and here you can see the vortex swirling on the ground. This video really shows off a C-17's huge vortex during landing.

Another beautiful C-17 vortex video.

Vortex Dissipators
Prevent vortices forming at the engine intakes which could cause gravel to be ingested by engine. These consist of a small forward projecting tube which blows pressure regulated (55psi) engine bleed air down and aft from 3 nozzles at the tip to break up the vortices.

Source

So basically it works by blowing air out of the tube to prevent vortices from forming. It is the vortex that sucks the stones up. No vortex = no FOD. The 'shield' kind of protection is installed on nose gear to prevent damage to the under belly.
**note main gear is behind engines so no FOD from main gear affect engines.

The key thing to realize here is that the main risk of FOD comes from a vortex (like a small tornado) forming ahead of the engine and bending to the ground and sucking the stones up. If such vortex is prevented, the stones won't come flying on their own.

Thanks @JanHudec. Already edit that to my answer. Feel free to improve it.

could you consider expanding your answer with additional information from that source you posted? in particular the image where the airflow from the 3 nozzles (and I thought it was only 1!) is shown is really interesting and educative. [said otherwise, I would be looking for a slightly more detailed "how"]


text:
Is there a database containing detailed information about airfields and runways?
Does an electronic database containing the various civil runways in a given region of the world exists?
Maybe even categorized by type (e.g., grass vs asphalt), length, if controlled or not, etc.
If it does not exists, what would be the effort related to creating one?
As Danny Beckett mentioned in comments, OurAirports has such data, but there is a "use at your own risk" disclaimer. May any source be reliable and trustworthy or will I find such disclaimer on all sources?

OurAirports has this data. I've personally only used it for the airport code/name data, so I don't know how complete the runway data is, but it's definitely worth checking!

@DannyBeckett had? the files seem to be empty.

eek!! someone shoot the webmaster (in all seriousness, I just sent them an email).

@DannyBeckett :D I will edit the question anyway, I'd rather find reliable data, not "use at your own risk" data

@DannyBeckett files on OurAirports have been restored :)

After a few years, I found the OurAirports still keeps updating airport data.

The “use at your own risk” warnings don’t mean they think the data is unreliable, just that they don’t guarantee that it’s reliable enough to bet the lives of a plane full of passengers. For that, you have to pay big bucks.

The FAA publishes the NASR database. This is an official, authoritative data set that covers all airports, airways, routes and navigation aids under FAA jurisdiction. The data files are not human-readable though and require special software to display.
Other civil aviation authorities in other countries have similar products. Some are available for free, some are not. Many countries claim intellectual property rights on their data and it can be quite difficult to get at/use it.
Some companies like Jeppesen do this collection for you: they have agreements with aviation authorities, obtain each authority's data sets (like the FAA's NASR linked above), and compile all of them into a single large database. This database is then reprocessed in forms usable by avionics like GPS receivers or Flight Management Systems (FMS). These countries charge a significant fee for this service, and there are licensing terms that limit your use of the data. The fee is substantial depending on the format you get the data in (up to thousands of dollars or more for FMS systems for large transport aircraft) and puts the dataset out of reach of a casual user.
The U.S. Department of Defense publishes the DAFIF which is a similar compilation of worldwide data. This database used to be available publicly for free, but is now restricted to Department of Defense personnel (it is not classified but it is not available to the public).
There are many websites based on one or more of the datasets above, but as noted in comments, these websites are not official or authoritative. They also generally have their own license terms that limit the way you can use the information and that prevent you from downloading the database in bulk. This all stems from the intellectual property claims made by many civil aviation authorities. It costs countries a lot of money to maintain the data and they want to be able to generate some revenue from it.
So the bottom line is that for some regions like the United States, official data is readily and freely available; for other regions, not so much. (And among developed countries, the U.S. is the exception; most do not offer their data freely.) To get data for these other regions, or to create a global dataset, would involve a lot of effort and money (beyond the reach of a normal individual). Companies that do this work for you charge hefty fees to provide the data to you.

A few years ago, I had a similar need for airport data from European countries, amongst which was Greece.
After going through a number of alternative resources, I settled for the data files of the flight simulator X-Plane.
X-Plane uses sime simple data files to define the position and characteristics of airports. See for example: http://data.x-plane.com/get_data.html
One of these datasets included the location, type of runway, airspace, runway orientation and comms freqs, practically for airports across the world.
The data is collected from various sources and kept up to date by the community. As far as Greece was concerned, all main airports of interest were described accurately enough.
Depending on the desired accuracy and purpose, you might find this database useful too.
Hope this helps.

I believe your answer comes with its own, built in, "use at your own risk" warning! Not that there's anything wrong with that.


text:
What's this black rectangle painted on the side of a V-1 flying bomb?
A friend sent me a photo of the V-1 flying bomb on display at the Air Zoo in Kalamazoo. What's the black painted rectangle on the side of the fuselage?

The writing isn't much help... Nicht auftreten is the German equivalent of "No step," but I don't know what Abstellpallung means, except that abstellen is "to cut off / shut down." I can't find Pallung in any German dictionary. The label appears to be pointing to the black rectangle, which appears to just be painted on.
I also can't find this rectangle in online V-1 photos.

Pallung: https://de.academic.ru/dic.nsf/dewiki/1072361

"abstellen" also means to put down something.

"Doppelpallung" appears in the print further back and translates as "double layering", which may refer to the outer shell of the vehicle.  The location of "abstellpallung N Herkules" could refer to the warhead?

it's just a "hard point" - exactly like the jack point on a car.

Any possibility the word is "Abstellpassung", using old german ortography rules that differentiate two types of "s", with the "other s" looking very much like "f" and by extension "l" in some fonts?

Do you know the Air Zoo of Kalamazoo ? Why yes, yes I do ! The Air Zoo of Kalamazoo !  I know of this place, this is true !  My only quandry, however, is whether or not Dr. Suess had frequented it too ?

A "Pallung" is a piece of wood (or something similar) that prevents ships (or something similar) from falling over when they are on land. "abstellen" means to put something down (such as luggage) or into storage. There are some recent articles that contain the word "Pallung" on google news, such as this one.
Assuming that the book depicted in this pdf is authentic, you can see what an Abstellpallung for a V1 looks like on page 29, indicated by the letters b and c:

Note that the text twice says "Markierung am Rumpf beachten!" (mind the markings on the fuselage), which probably corresponds to the black rectangles mentioned by the OP.

(Some native German users have indicated that they have never heard the word. Neither have I, until today. I am not sure about other languages, but in German, some domains have very specific vocabulary that a layman will almost never get in contact with. One example of this is anything connected with ships, another one is hunting, and there are probably some more. The manual contains another example just in the preceding sections (what does "heißen" mean here?). So "I have never heard the word" may just mean that someone is not familiar with some particular domain.)

Nice find! Please do add the image, as it seems to provide exactly the answer to the question. And, welcome to av.se!

@Jan German "heißen" also can means to hoist, used for handling heavy objects. For hoisting a flag or sail, the german word is "hissen" - looks like a common root.

Oh wow. I looked at the media in that category on Commons, I did not notice the PDFs with multiple pages.

@Bobby: I was able to figure out the meaning on my own (because of the pictures), but not the possible common root. Thanks

so if I'm reading this correctly those black rectangles are "rest points" or something? as in "rest the device on blocks at these points"?

@jcollum Correct.

I have encountered the word Abstellpallung before in aviation. It is sometimes used for the struts/brackets/frame used to hold the (detachable) wings of a sailplane during storage or transport. Most German sailplane jockeys of my acquaintance use the word frame or bracket nowadays, but I have heard Abstelpallung from some elderly fellows.

abstellen is "to cut off / shut down."

That's one meaning of the word, what we need here is "putting down", "parking" or "putting in storage".

I don't know what Abstellpallung means. I can't find Pallung in any German dictionary.

Me neither. It seems to be a quite rare nautical term, meaning "strutting", "bracing" or "propping"1. A "Palle" is a (wooden) support block on which ships would rest in a dry dock.
The closest match I found in an actual dictionary is the adjective "pall" from the Low German language [1] [2] which means "steif" or "fest" (stiff/firm) in German, and certainly could also be used as a verb ("make firm", to strut). Even the Duden knows the noun "Pall" from the same word origin, as nautical term for a pawl (ratchet) that fastens a capstan.

What's the black painted rectangle on the side of the fuselage?

It appears to be the point where the fuselage is meant to rest on a support frame for storage. I would guess that location is reinforced by the internal structure2, like @PeterKämpf said, for jacking it up.
1: Not sure what the subtle differences between these terms are, I'm not a native English speaker.
2: Or not.

Strutting: is to brace something (so equivalent to “bracing”) (but rarely used). Bracing: making a structure firmer with additional forms of support. Generally considered to be extra support in addition to some existing structure. Propping: the most accurate word here I think, meaning using an object to keep something in position. Said object is considered a “prop”; for example, in construction one would use an “Acrow prop” to temporarily hold a wall, perhaps.

@Tim Thanks! Another term I found is shoring. I think in this case it is indeed additional support that's only used when in storage. We can also find on some images "Rollpallung" and "Doppelpallung", the points where it is cradled on a roll cart for moving (Wikimedia Commons has some original pictures of that).

By the way, German nautical terms being of Low German origin is neither rare nor coincidental. It also explains why they seem strange to many Germans.

Contrary to some other answers Palle is actually a real German word, though it is used mostly in context of shipyards. A Palle is a wooden or concrete block on which ships are resting in drydock.
See also this German Wikipedia entry:
https://de.wikipedia.org/wiki/Palle
A 'Abstellpallung' thus means a location one the V-1 where one can safely support it on a Palle for storage or maintenance. The black rectangle marks that location.

Sounds like English "pallet" which many people will think means an artists pallet (for paint) but more broadly is a (usually wooden) structure for carrying something else. Pallets are very commonly used for all kinds of shipping of goods.

@UuDdLrLrSs The last thing I would think of when hearing pallet is the board an artist uses to hold their paint.

@DKNguyen maybe I watched too much Bob Ross when I was a kid :)

@UuDdLrLrSs Less Bob Ross, more part time jobs as kid.

@DKNguyen ironically I have loads of pallets now, for stacking firewood and stuff. But I do very little painting!

@UuDdLrLrSs - note that an artists paint palette is spelled TTE. (This word is also commonly used by computer programmers / filmmakers etc in relation to the color palette available.)  Spelling paint palette with LLET would look very wrong.  The wooden thing you find on trucks is LLET.  This can be easily checked in the OED built-in to any Mac, or, just google.

@Fattie I suppose -ette came from French into English, maybe? Nonetheless they may all share the same root.

@UuDdLrLrSs just trying to cut down the confusion in this QA - your first sentence is "English "pallet" which many people will think means an artists pallet" which is wrong.  When any native English speaker sees "pallet" they think of fork lifts and trucks.  The sentence fragment "an artists pallet" looks like a spelling mistake or typo.  (By all means when you hear the two words, obviously they are homophones.)

@Fattie you're right, it was a typo which I didn't realize. One reminded me of the other and I didn't notice the misspelling.

Note that normally of course nobody would make comments on trivial spelling mistakes / typos in comments!   But I was just mentioned it since the very nature of this page is about a subtle spelling problem indeed in another language - for example, a German-speaker may read our comments here and be Clarified!  :)   Cheers

"Abstellpallung" isn't a word in German.
If you search the web for this word, you will find lots of links to the V-1, and it seems this word has been exclusively used on restored V-1 in several museums. But nowhere else.
The conclusion is clear: This is the result of a poor restoration and everyone seems to have copied this from its original source. Which was not a V-1, but some ignorant restorer.
Edit: I stand corrected. While extremely unusual, Palle or Pallung seems to be used for wooden blocks on which a ship rests. But outside of restored V-1s in museums it is not used in the context of German WW II aircraft, as fas as I know. I'd be interested to see evidence to the contrary, though.
You will also see that the original word at this location is "Hier aufbocken Auf Abstellbock" which is proper German (except for the capital A in Auf) and means "Jack up here on parking trestle". But even the vey unusual "Abstellpallung" will be found, but at a much more forward location.

V-1 in the Imperial War Museum, Duxford (picture source)

I have to disagree. While "Pallung" is not a common word, it still seems to be a valid German nautical word. A definition I found at https://www.tis-gdv.de/tis/taz/p/pallung-htm/: "Pallung ist aber auch die Bezeichnung für Stapelhölzer, auf denen ein Schiff im Dock oder auf der Helling liegt." Wikipedia does know a "Palle", and the -ung form for the usage of said pieces is not really far fetched.

If you search for "Pallung" on google news, you can find some German newspaper articles (and a few indonesian ones) that contain the word. Incidentically, most of these articles seem to be from areas that are not that far from Peenemünde (Wolgast and Rostock)

@Jan, yes it is. A very common sign in Germany is "Rasen nicht betreten!" → "do not step onto the lawn" (better: keep off the grass). No matter how careful you are. ;-)

Old photo of V1 with what looks to me like a "Nicht auftreten" caption (but without "Pallung", possibly because it has been photographed from the other side): https://commons.wikimedia.org/wiki/Category:V-1#/media/File:Place_de_la_mairie_V1_22_sept_1945_5618.JPG

@Taschi, "auftreten" is fine here I'd say. Feels a bit archaic to me but is even nowadays used in that sense, eg. in https://gelenk-klinik.de/fuss/fussschmerzen-fersenschmerzen.html or https://www.sportega.de/s/laufschuhe-drop-auftreten-2365

In Nazi-Germany there were words in the (technical) vocabulary that are no longer in use today and that have been Anglicized, especially in the field of aircraft technology.  'Abstellpallung' just means 'storage cradle'.

Jan posted the correct answer - although it needs some rework when he is back on desktop. In that document the word is mentioned quite often and it seems pretty authentic.

Abstellpallung means storage pallet in English, there is a similar marking on the right side opposite that one in the picture as well as left and right rear. These are likely the places where the storage/transport pallet was supposed to contact the weapon structure.

@Taschi The Duden does know "Pall", with origin "niederdeutsch, zu: pal(l) = steif, fest", so a meaning of "Versteifung"/"Aussteifung" doesn't seem wrong.

@Taschi But yeah, it doesn't mean "pallet" for sure. I'd probably translate it as strutting or bracing.

Amazing how these translations are not exact because the English word is different.  A pallet is obviously a "storage support": Abstellpallung.  Pallets are made to keep product from being in contact with the ground, and for ease of movement (with fork lifts).

You can just make out the writing (unreadable) and downward pointing arrow on this photograph.
Source https://www.historyanswers.co.uk/wp-content/uploads/2014/11/Credi-Bundesarchiv-Bild-146-1973-029A-24A-Lysiak-CC-BY-SA.jpg

This second photo shows the other side (different personnel so not a mirror image). This supports the idea of it indicating a a pair of strong points for storage.

In the second photo, you can see what appears to be pale-coloured writing on the section just after the nose cone.  Maybe an image processing expert could help.
I'll try asking on a suitable stack exchange!

Finally - this photo  shows what is claimed to be a 1944 photo of a much cruder-looking missile. If there is any writing in that area, it appears to be hand-painted.

Otherwise, great info! +1

@FreeMan - Have I done it right? Or should there be more description?

Excellent. By hovering, I can see that it's a gettyimmages.com link.

Amazing info here !